The present invention relates to an automotive transmission, and more particularly to a transmission of the countershaft type.
There are many automotive transmission of the countershaft type having first through third parallel shafts, a plurality of trains of intermeshing transmission gears, and clutching means (engaging/disengaging means) such as hydraulic clutches, synchromesh mechanisms, or the like for selecting power transmission via any one of the transmission gear trains, the gears and the clutching means being disposed parallel to each other in the axial direction. Engine output power which has been changed in speed by the transmission gear train selected by the clutching means is transmitted to the third shaft (see Japanese Patent Publication No. 62-34979, for example).
The transmission gears in such countershaft-type transmissions are arranged in various designs dependent on whether the engine is directed longitudinally or transversely with respect to the automobile.
An automatic transmission of the countershaft type for use with an engine directed transversely in an engine compartment is shown in FIG. 6 of the accompanying drawings. The transmission, generally designated by the reference numeral 70, has an input shaft 72 disposed on a first shaft coaxially with and engageable with and disengageable from an output shaft (flywheel) 2a of an engine 2 through a main clutch 71, and a countershaft 73 and an output shaft 74 disposed respectively on second and third shafts lying parallel to the first shaft. The transmission 70 also includes five trains of intermeshing transmission gears 81a, 81b; 82a, 82b; 83a, 83b; 84a, 84b; 85a, 85b and synchromesh mechanisms 76 through 78, all disposed between the input shaft (first shaft) 72 and the countershaft (second shaft) 73 and parallel to each other in the axial direction. Any one of the synchromesh mechanisms 76 through 78 is operated to select one of the transmission gear trains for power transmission and speed changing. The engine output power thus changed in speed is transmitted through output gears 89a, 89b to the output shaft (third shaft) 74, from which drive power is transmitted to lefthand and righthand road wheels.
FIG. 7 shows an automatic transmission of the countershaft type for use with an engine directed longitudinally in an engine compartment. The transmission, generally designated by the reference numberal 90, has an input shaft 92a disposed on a first shaft coaxially with and engageable with and disengageable from an output shaft (flywheel) 2a of an engine 2 through a main clutch 91, and a second countershaft 92b disposed on the first shaft and engageable with and disengageable from the input shaft 92a. The transmission 90 also has a first countershaft 93 and an output shaft 94 disposed respectively on second and third shafts lying parallel to the first shaft. The transmission 90 also includes a train of intermeshing input gears 101a, 101b disposed between the input shaft 92a and the first countershaft 93, five trains of intermeshing transmission gears 102a, 102b; 103a, 103b; 104a, 104b; 105a, 105b; 106a, 106b and synchromesh mechanisms 96 through 98, all disposed between the second countershaft (first shaft) 92b and the first countershaft (second shaft) 93 and parallel to each other in the axial direction. Any one of the synchromesh mechanisms 96 through 98 is operated to select one of the transmission gear trains for power transmission and speed changing. The engine output power thus changed in speed is transmitted through output gears 109a, 109b, 109c to the output shaft (third shaft) 94, from which drive power is transmitted to front and rear road wheels.
The transmissions described above have large axial dimensions since the plurality of the trains of transmission gears and the synchromesh mechanisms (hydraulic clutches may be employed in place of the synchromesh mechanisms) for selecting one of the gear trains are disposed between the first and second shafts and lie parallel to each other in the axial direction. The more the gear positions of the transmission, the greater the axial dimension thereof.
With the transmission being directed transversely in the engine compartment, if the axial dimension of the transmission is large, any margin of the installation space available in the engine compartment for the transmission is small. Where the transmission is directed longitudinally in the engine compartment, if the axial dimension of the transmission is large, it suffers from the problem of a reduced passenger compartment space in addition to the above problem of the reduced margin of the installation space in the engine compartment. Another drawback is that the shafts of the transmissions are longer and have reduced rigidity, increasing noise from the gears on the shafts and reducing gear durability. Furthermore, the rigidity of the transmission case is lowered and hence vibration and noise of the power line are increased.